Cellular telephone systems and other portable electronic devices of different manufacture each have their own particular operating characteristics. Meeting these diverse requirements has presented a challenge for component manufacturers. For example, manufacturers of memories for the wireless and portable electronic device market typically offer a variety of memory devices to meet the specifications for different manufacturers. Accordingly, the development and production cost of memory devices for such applications is significantly affected.
One application requirement that varies widely among cellular telephone system manufacturers is the main power supply voltage. While most cellular telephone manufactures have migrated to very low power platforms (VCC=1.65V-2.0V) a large number of applications still require a 3V input output (I/O) interface (VCCQ=2.7V-3.3V). As a consequence, flash memory manufactures typically offer, in addition to full low-voltage devices having both the memory core and I/O interface powered at 1.8V, mixed-power supply devices having a 1.8V main power supply and a 3V I/O interface. Moreover, in the future, manufacturers may decide to migrate to systems having even lower main power supply voltages. Since full low-voltage and mixed-voltage devices typically use different I/O buffer circuits, the two versions essentially present two different design projects and their fabrication requires the generation of two different sets of masks.
Another application requirement that varies from one cellular system to another is I/O load impedance. The large variability of load transmission line characteristics, i.e., the capacitance, inductance, and resistance of the load, renders it very difficult to optimize buffer drive strength. For example, drive strength adequate for a 30 pF load, may result in a noisy output signal due to signal ringing. Signal ringing must of course be avoided while still switching as fast as possible to meet the high-speed performance requirements of modern integrated circuits and designs. The above-mentioned problems, as well as other problems, are addressed at least in part by the present invention and will be understood by reading and studying the following specification.